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: 92634125 ("memstick: add driver for Ricoh R5C592 card reader")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230516202714.560929-1-arnd@kernel.orgSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>