Revert "swiotlb: panic if nslabs is too small"

Revert "swiotlb: panic if nslabs is too small"

This reverts commit cd13b21a12adc1a849f825b47ea33ee25df845c8.

Reasons:
  1. new panic()s shouldn't be added [1].
  2. It does no "cleanup" but breaks MIPS [2].

v2: properly solved the conflict [3] with
commit e458adef91f32 ("swiotlb: split up the global swiotlb lock")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
[1] https://lore.kernel.org/r/CAHk-=wit-DmhMfQErY29JSPjFgebx_Ld+pnerc4J2Ag990WwAA@mail.gmail.com/
[2] https://lore.kernel.org/r/20220820012031.1285979-1-yuzhao@google.com/
[3] https://lore.kernel.org/r/202208310701.LKr1WDCh-lkp@intel.com/

Fixes: cd13b21a12adc ("swiotlb: panic if nslabs is too small")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>