dma: ipu: ipu_idmac: Fix section mismatch

Since commit 84c1e63c12 (dma: Remove erroneous __exit and __exit_p() references)
the following section mismatch happens:

WARNING: drivers/built-in.o(.text+0x20f94): Section mismatch in reference from the function ipu_remove() to the function .exit.text:ipu_idmac_exit()
The function ipu_remove() references a function in an exit section.
Often the function ipu_idmac_exit() has valid usage outside the exit section
and the fix is to remove the __exit annotation of ipu_idmac_exit.

Remove the '__exit' annotation from ipu_idmac_exit in order to fix it.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Maxin B. John <maxin.john@enea.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>