Documentation: Update path to sysrq.txt

Commit 9d85025b0418 ("docs-rst: create an user's manual book") moved the
sysrq.txt leaving old paths in the kernel docs.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Mauro Carvalho Chehab <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/media/v4l-drivers/bttv.rst

···
 protection faults (so-called "kernel oops").
 
 If you run into some kind of deadlock, you can try to dump a call trace
-for each process using sysrq-t (see Documentation/sysrq.txt).
+for each process using sysrq-t (see Documentation/admin-guide/sysrq.rst).
 This way it is possible to figure where *exactly* some process in "D"
 state is stuck.
 

Documentation/s390/Debugging390.txt

···
 This is particularly useful for syncing disks unmounting & rebooting
 if the machine gets partially hung.
 
-Read Documentation/sysrq.txt for more info
+Read Documentation/admin-guide/sysrq.rst for more info
 
 References:
 ===========

Documentation/sysctl/kernel.txt

···
 - softlockup_all_cpu_backtrace
 - soft_watchdog
 - stop-a                      [ SPARC only ]
-- sysrq                       ==> Documentation/sysrq.txt
+- sysrq                       ==> Documentation/admin-guide/sysrq.rst
 - sysctl_writes_strict
 - tainted
 - threads-max

Documentation/virtual/uml/UserModeLinux-HOWTO.txt

···
 
   This takes one argument, which is a single letter.  It calls the
   generic kernel's SysRq driver, which does whatever is called for by
-  that argument.  See the SysRq documentation in Documentation/sysrq.txt
-  in your favorite kernel tree to see what letters are valid and what
-  they do.
+  that argument.  See the SysRq documentation in
+  Documentation/admin-guide/sysrq.rst in your favorite kernel tree to
+  see what letters are valid and what they do.