tools/rv: Fix curr_reactor uninitialized variable

clang is reporting:

$ make HOSTCC=clang CC=clang LLVM_IAS=1

clang -O -g -DVERSION=\"6.8.0-rc3\" -flto=auto -fexceptions
-fstack-protector-strong -fasynchronous-unwind-tables
-fstack-clash-protection -Wall -Werror=format-security
-Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS
$(pkg-config --cflags libtracefs) -I include
-c -o src/in_kernel.o src/in_kernel.c
[...]

src/in_kernel.c:227:6: warning: variable 'curr_reactor' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
227 | if (!end)
| ^~~~
src/in_kernel.c:242:9: note: uninitialized use occurs here
242 | return curr_reactor;
| ^~~~~~~~~~~~
src/in_kernel.c:227:2: note: remove the 'if' if its condition is always false
227 | if (!end)
| ^~~~~~~~~
228 | goto out_free;
| ~~~~~~~~~~~~~
src/in_kernel.c:221:6: warning: variable 'curr_reactor' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
221 | if (!start)
| ^~~~~~
src/in_kernel.c:242:9: note: uninitialized use occurs here
242 | return curr_reactor;
| ^~~~~~~~~~~~
src/in_kernel.c:221:2: note: remove the 'if' if its condition is always false
221 | if (!start)
| ^~~~~~~~~~~
222 | goto out_free;
| ~~~~~~~~~~~~~
src/in_kernel.c:215:20: note: initialize the variable 'curr_reactor' to silence this warning
215 | char *curr_reactor;
| ^
| = NULL
2 warnings generated.

Which is correct. Setting curr_reactor to NULL avoids the problem.

Link: https://lkml.kernel.org/r/[e-mail]

Cc: [e-mail]
Cc: Masami Hiramatsu <[e-mail]>
Cc: Nathan Chancellor <[e-mail]>
Cc: Nick Desaulniers <[e-mail]>
Cc: Bill Wendling <[e-mail]>
Cc: Justin Stitt <[e-mail]>
Cc: Donald Zickus <[e-mail]>
Fixes: 6d60f89691fc ("tools/rv: Add in-kernel monitor interface")
Signed-off-by: Daniel Bristot de Oliveira <[e-mail]>

tools/verification/rv/src/in_kernel.c

···
 static char *ikm_get_current_reactor(char *monitor_name)
 {
 	char *reactors = ikm_read_reactor(monitor_name);
+	char *curr_reactor = NULL;
 	char *start;
 	char *end;
-	char *curr_reactor;
 
 	if (!reactors)
 		return NULL;