efi/gop: Remove redundant current_fb_base

current_fb_base isn't used for anything except assigning to fb_base if
we locate a suitable gop.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200320020028.1936003-2-nivedita@alum.mit.edu


Signed-off-by: Ard Biesheuvel <ardb@kernel.org>