drivers/video/backlight/ep93xx_bl.c: add missing include of linux/module.h

ep93xx_bl.c uses interfaces from linux/module.h, so it should include
that file.  This patch fixes build errors:

    CC [M]  drivers/video/backlight/ep93xx_bl.o
  drivers/video/backlight/ep93xx_bl.c:138: error: 'THIS_MODULE' undeclared here (not in a function)
  drivers/video/backlight/ep93xx_bl.c:158: error: expected declaration specifiers or '...' before string constant
  drivers/video/backlight/ep93xx_bl.c:158: warning: data definition has no type or storage class
  ...

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>