spi: bcm-qspi: don't include linux/mtd/cfi.h

The header isn't actually needed here, but including it leads
to a build warning when CONFIG_MTD is disabled:

include/linux/mtd/cfi.h:76:2: #warning No CONFIG_MTD_CFI_Ix selected. No NOR chip support can work. [-Werror=cpp]

Fixes: fa236a7e

 (spi: bcm-qspi: Add Broadcom MSPI driver)
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>