drivers: misc: Mark function jp_generic_ide_ioctl() as static in lkdtm.c

This patch marks the function jp_generic_ide_ioctl() as static in
lkdtm.c because it is not used outside this file.

Thus, it also eliminates the following warnings in lkdtm.c:
drivers/misc/lkdtm.c:227:5: warning: no previous prototype for ‘jp_generic_ide_ioctl’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>