spi: spi-zynqmp-gqspi: Fix missing unlock on error in zynqmp_qspi_exec_op()

spi: spi-zynqmp-gqspi: Fix missing unlock on error in zynqmp_qspi_exec_op()

[ Upstream commit 6043357263fbe2df0bf0736d971ad5dce7d19dc1 ]

Add the missing unlock before return from function zynqmp_qspi_exec_op()
in the error handling case.

Fixes: a0f65be6e880 ("spi: spi-zynqmp-gqspi: add mutex locking for exec_op")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210412160025.194171-1-weiyongjun1@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>