'cxl_context_alloc()' does not return an error pointer. It is just a
shortcut for a call to 'kzalloc' with 'sizeof(struct cxl_context)' as the
size parameter.
So its return value should be compared with NULL.
While fixing it, simplify a bit the code.
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
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