pxafb: lcsr1 is unused without CONFIG_FB_PXA_OVERLAY

Fixes the warning:

  drivers/video/pxafb.c: In function 'pxafb_handle_irq':
  drivers/video/pxafb.c:1442: warning: unused variable 'lcsr1'

[akpm@linux-foundation.org: save an ifdef]
Signed-off-by: Denis V. Lunev <den@openvz.org>
Cc: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>