drivers: spi: Fix compiler warning

Addresses "warning: cast from pointer to integer of different size".

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
12 jobs for next in 22 minutes and 31 seconds (queued for 2 minutes and 51 seconds)
Status Job ID Name Coverage
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arm-4.14-release

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x86-5.4-head

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