spi: bcm63xx: fix max prepend length

stable inclusion
from stable-v5.10.188
commit 6e88cc510f2706462210abb6adce4bdf8521a6cf
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8KYFP

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6e88cc510f2706462210abb6adce4bdf8521a6cf



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[ Upstream commit 5158814c ]

The command word is defined as following:

    /* Command */
    #define SPI_CMD_COMMAND_SHIFT           0
    #define SPI_CMD_DEVICE_ID_SHIFT         4
    #define SPI_CMD_PREPEND_BYTE_CNT_SHIFT  8
    #define SPI_CMD_ONE_BYTE_SHIFT          11
    #define SPI_CMD_ONE_WIRE_SHIFT          12

If the prepend byte count field starts at bit 8, and the next defined
bit is SPI_CMD_ONE_BYTE at bit 11, it can be at most 3 bits wide, and
thus the max value is 7, not 15.

Fixes: b17de076 ("spi/bcm63xx: work around inability to keep CS up")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Link: https://lore.kernel.org/r/20230629071453.62024-1-jonas.gorski@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>