memstick r592: make memstick_debug_get_tpc_name() static

There are no other files referencing this function, apparently
it was left global to avoid an 'unused function' warning when
the only caller is left out. With a 'W=1' build, it causes
a 'missing prototype' warning though:

drivers/memstick/host/r592.c:47:13: error: no previous prototype for 'memstick_debug_get_tpc_name' [-Werror=missing-prototypes]

Annotate the function as 'static __maybe_unused' to avoid both
problems.

Fixes: 926341250102 ("memstick: add driver for Ricoh R5C592 card reader")
Signed-off-by: Arnd Bergmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/memstick/host/r592.c

···
  * memstick_debug_get_tpc_name - debug helper that returns string for
  * a TPC number
  */
-const char *memstick_debug_get_tpc_name(int tpc)
+static __maybe_unused const char *memstick_debug_get_tpc_name(int tpc)
 {
 	return tpc_names[tpc-1];
 }
-EXPORT_SYMBOL(memstick_debug_get_tpc_name);
-
 
 /* Read a register*/
 static inline u32 r592_read_reg(struct r592_device *dev, int address)