mmc: update sdio_claim_irq documentation

Update documentation for sdio_claim_irq to downgrade the wording
about doing recursive claims in an IRQ handler from 'must not' to
'should not'. This clarifies that recursive claims are supported,
but not the recommended (best) practice

Signed-off-by: Joel Cunningham <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/core/sdio_irq.c

···
  *
  *	Claim and activate the IRQ for the given SDIO function. The provided
  *	handler will be called when that IRQ is asserted.  The host is always
- *	claimed already when the handler is called so the handler must not
- *	call sdio_claim_host() nor sdio_release_host().
+ *	claimed already when the handler is called so the handler should not
+ *	call sdio_claim_host() or sdio_release_host().
  */
 int sdio_claim_irq(struct sdio_func *func, sdio_irq_handler_t *handler)
 {