ms5611: change bus speed to 5MHz
ms5611: change bus speed to 5MHz

this gives 5MHz SPI bus speed (by asking for 6MHz due to timer
granularity).

Tests with a logic analyser show that the ms5611 is actually more
reliable at 5MHz than lower speeds

jlecoeur/Firmware,krbeverx/Firmware,acfloria/Firmware,Aerotenna/Firmware,PX4/Firmware,jlecoeur/Firmware,acfloria/Firmware,jlecoeur/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,darknight-007/Firmware,jlecoeur/Firmware,dagar/Firmware,Aerotenna/Firmware,mcgill-robotics/Firmware,PX4/Firmware,krbeverx/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,darknight-007/Firmware,PX4/Firmware,acfloria/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,dagar/Firmware,Aerotenna/Firmware,PX4/Firmware,dagar/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,darknight-007/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,jlecoeur/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,darknight-007/Firmware,dagar/Firmware,darknight-007/Firmware,dagar/Firmware,dagar/Firmware,Aerotenna/Firmware,krbeverx/Firmware,mcgill-robotics/Firmware,dagar/Firmware,Aerotenna/Firmware