dmaengine: idxd: Remove a useless mutex

ida_alloc()/ida_free() don't need any mutex, so remove this one.

It was introduced by commit e6fd6d7e ("dmaengine: idxd: add a device to
represent the file opened").

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/e08df764e7046178ada4ec066852c0ce65410373.1730547933.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Vinod Koul <vkoul@kernel.org>