fbdev: chipsfb: remove set but not used variable 'size'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/video/fbdev/chipsfb.c: In function 'chipsfb_pci_init':
drivers/video/fbdev/chipsfb.c:352:22: warning:
 variable 'size' set but not used [-Wunused-but-set-variable]

Fixes: 8c870933 ("[PATCH] ppc32: Remove CONFIG_PMAC_PBOOK").
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
[b.zolnierkie: minor commit summary and description fixups]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>