fb: make fp_get_options name argument const

fb: make fp_get_options name argument const

drm_get_connector_name now returns a const value, which causes the following
compilation warning:

  drivers/gpu/drm/drm_fb_helper.c: In function ‘drm_fb_helper_parse_command_line’:
  drivers/gpu/drm/drm_fb_helper.c:127:3: warning: passing argument 1 of ‘fb_get_options’ discards ‘const’ qualifier from pointer target type [enabled by default]
  In file included from drivers/gpu/drm/drm_fb_helper.c:35:0:
  include/linux/fb.h:627:12: note: expected ‘char *’ but argument is of type ‘const char *’

As fb_get_options uses its name argument as read only, make it const. This
fixes the aforementioned compilation warning.

Signed-off-by: Vincent Stehlé <vincent.stehle@freescale.com>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: trivial@kernel.org
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>