Bluetooth: shell: Fix floating point usage

Avoid floating point usage when possible. E.g. on qemu_x86 this would
otherwise result in something like the following:

<err> os: Floating point unit not enabled
<err> os: eax: 0x00000024, ebx: 0x00000000, ecx: 0x00248fc8,
          edx: 0x00146120
<err> os: esi: 0x0012b30c, edi: 0x0024c628, ebp: 0x0024c638,
          esp: 0x0024c5b8
<err> os: eflags: 0x00000216 cs: 0x0008 cr3: 0x001465a0
<err> os: call trace:
<err> os: eip: 0x00121c8d
<err> os:      0x0010679c (0x127750)
<err> os:      0x0010693b (0x100f33)
<err> os:      0x001061bc (0x12b800)
<err> os:      0x001074fb (0x0)
<err> os:      0x00101151 (0x12b800)
<err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception
<err> os: Current thread: 0x00146120 (shell_uart)
<err> os: Halting system

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>